The best way I know of to get all the "stuff" out of your cooling system, would be to get one of those Prestone Reverse Flush Kits. You just splice a tee fitting into one of the heater hoses(I forget which one at the moment) and connect your garden hose to it and flush away. I think it works best if you temporarily remove the thermostat when your doing the reverse flush but I don't think it is necessary. Then again, if you haven't replaced your thermostat in awhile, and your going though all this time and expense to flush out your system, now is the time to replace it along with your upper and lower radiator hoses and clamps. I would think that after you flushed out the cleaning solution and filled the car just with water one more time, let it cirulate for about 5 to 10 minutes, drain it, and you should be good to go with Dex-Cool. Check your manual for the capacity of your cooling system(mine is 13 quarts). You're not going to get ALL of the water out of your system(some stays in the block and heater core). So after you drain most of it out, add your Dex-Cool(again for me it would be 6 1/2 quarts) and the rest will be water so you have a 50% mixture. Don't forget that the cooling system has to be bled(ie. purged of air) so keep the radiator cap off while the engine is running. Also, there are some purists that believe that you should ONLY use Distilled Water when refilling your system. I'm not one of them but I just wanted to keep your options open.
2006 Salsa Vibe
2002 Snap Orange Beetle - Turbo
1991 Olds "Orphaned" 88 - Donated to Science!